(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Architectural and engineering factors in solar systems design"

■jji . NJULftK /UfiWU 



— / « / /<-> 






SOLAR/0800-78/70 
DISTRIBUTION CATEGORY UC-59 





Architectural and Engineering 

Factors in 
Solar Systems Design 

July 15, 1978 



Work Performed Under Contract No. EG-77-C-01-4049 




U.S. Department of Energy 



National Solar Heating and 
Cooling Demonstration Program 

National Solar Data Program 



NOTICE 

This report was prepared as an account of work sponsored by the United States 
Government. Neither the United States nor the United States Department of Energy, nor 
any of their employees, nor any of their contractors, subcontractors, or their employees, 
makes any warranty, express or implied, or assumes any legal liability or responsibility for 
the accuracy, completeness or usefulness of any information, apparatus, product or process 
disclosed, or represents that its use would not infringe privately owned rights. 



This report has been reproduced directly from the best available copy. 



Available from the National Technical Information Service, U. S. Department of 
Commerce, Springfield, Virginia 22161. 



Price: Paper Copy S4.00 
Microfiche $3.00 



A key part of the national solar demonstration program is the acquisition and dissemina- 
tion of data generated by the demonstration projects. The Ehrenkrantz Group, Architects 
and Planners, as a subcontractor to PRC Energy Analysis Company under contract to the 
Department of Energy, has been involved in this process for more than a year. The 
following paper, based on the review and analysis of over 70 projects, will focus on some 
of the most common design and construction problems. Structural details and specifica- 
tions and some trade-offs that can make for a more cost-effective project will be 
addressed rather than mechanical considerations, such as collector selection. 



ECONOMIC CONSIDERATIONS 

THE SOLAR DESIGNER 
IS WORKING WITH 
RELATIVELY LOW 
LEVELS OF THERMAL 
ENERGY. 

THIS LIMITS THE AMOCINT 
OF MONEY THAT CAN 
BE PRUDENTLY 
EXPENDED ON THE 
COLLECTION AND 
TRANSPORT OF SOLAR 
ENERGY. 



The whole solar installation must be 
value-engineered to arrive at the lowest 
first cost consistent with quality of mate- 
rials and workmanship required. The 
desire to extract every theoretical Btu 
from a system often leads to the installa- 
tion of extra devices that will not be 
cost-effective and will only increase the 
payback period of the project. 



CONSTRUCTION 
CONSIDERATIONS 



If we look out over a typical residential or 
commercial building roofscape we see a 
minimal amount of exposed construction, 
especially piping. As a result, the build- 
ing trades , cannot be expected to bring 
prior experience to bear in solving typical 
problems that accompany solar projects 
with their large amount of exposed exter- 
ior construction. 



SOLAR COLLECTION SYSTEMS 
TYPICALLY REQUIRE 
CONSIDERABLY MORE 
EXPOSED EXTERIOR 
CONSTRUCTION THAN THE 
BUILDING TRADES ARE 
ACCUSTOMED TO 

THEREFORE, THE DESIGNER 
MUST ISOLATE AND SOLVE 
CONSTRUCTION PROBLEMS 
AND NOT LEAVE DECISIONS 
TO THE CONTRACTOR. 



Layout and Access vs. Cost— Some considerations that have an impact on costs involve the 
collectors and structural layouts and the degree of accessibility provided to the collectors 
and piping for servicing. The designer feels that immediate access to all parts of the 
array is mandatory, especially in the case of evacuated tube designs. One of the more 
handsome designs we have seen provides accessibility to each row of collectors. 



*S \ -v 

— a L 



-^ % N x «v *. 



A 



Each row of collectors is slightly higher than the one in front of it, with accessibility to 
piping and collectors in the form of a walkway at each location. This makes the system 
both extremely accessible and extremely expensive. The large amount of miscellaneous 
metal that goes into this design is very expensive and has delayed the project. 



Simpler and less expensive approaches would extend the array to the full extent of the 
available space provided by the structure, simplify the design of the collector support, and 
eliminate the walkways. 



^ 5. k 6> 



i=^ 



One can see that by changing the level of the structure only slightly, it would be possible 
to simplify the installation. 





N K 



Jrt 



Another approach would be to double up the last two rows of collectors and keep the 
structure level. 



In either case, by keeping the whole structure near the roof, accessibility could have been 
provided with a ladder rather than with walking surfaces. 



I like to call the next design the "O.S.H.A. Special." Notice that ladders have been 
provided as well as walkways and handrails. Again, this is extremely expensive. In this 
particular project, which was built by Unistrut, the structure is much too flexible, and the 
collector will leak if there is any movement in the structure. 



A much less expensive, faster, and easier 
alternative would have been to place two 
single rows of collectors (as noted in the 
circle) on the roof— assuming there is suf- 
ficient space available. The simpler 
structure would be sufficiently rigid, and 
access would be from the roof. 



5USwS8Pfe ewr 




Cost of Space Frames and Special 
Shapes vs. Standard Steel Shapes— 
Another cost trade-off involves the 
design of the collector support. It 
seems that when the requirements for 
triangular support and fairly long 
spans are presented, the first things 
that come to the designer's mind are 
special shapes and space frames. In 
one case, it's an aluminum tube space 
frame; in another case, it's a square 
tube steel frame. Both will be hand- 
some structures, if one can afford to 
build them. However, a much more 
efficient and less expensive approach 
is the use of simple, rolled-steel, angle 
sections with steel beams for the ma- 
jor span. 







POUND 

aluminum 
we*. 



56UARE STfcfcL Tbftfc 
6PACE FMME 





HOT RPU£D SUtNDMD 
3rUL96CTI0NS- 

66AM CDNeTftlCTK*! 



Support Trade-offs — Col lec- 
tor supports ultimately must 
be tied down to the roof 
structure. Designers have 
decided, in some cases to 
try to avoid penetrating the 
roofing. In this illustration, 
you see an attempt to span 
between a wall and a para- 
pet to avoid penetrating the 
roofing. After a review, it 
was discovered that $40,000 
could be saved by putting in 
two pitch pockets 12.5 feet 
on center, rather than a 27 
WF steel beam 12 feet on 
center. 



it 



Lj^ 



i 



pneH 



■2Y 



12-0 
OC- 



h 



I I2'«. 



The structure presented in 
the adjacent illustration 
could not take any point 
loads. As a result, the de- 
signers tried to distribute 
the load over the whole 
structure by using 700 pitch 
pockets. The probability 
that this structure will leak 
is quite high. 



V 



st;; 



[3 t tl I) 



V6 



i) i) [) ii 

i) ii ii 

n ii ii n 

II I) U II i 

II tl II 



turner 




Once you have decided on your basic 
structural approach, the next question is 
how to anchor it down. You can use 
regular pitch pockets, curbs constructed 
in the field, manufactured curbs or (if 
your vertical support is c regular shape, 
such as square or rouno,/ a neoprened 
sleeve. There is also a simple sleeper 
that can be bolted down. 



prt&Mwwsr 



cm* 





I 




erne 




fflPjLJlk 



<umK 



•zr \ r\ i -\ n_,". r\ ncr\ 



In some designs there has been an attempt to minimize or eliminate roofing penetrations. 



For example, in this case the designer was 
working with a light frame structure, 
using sleepers not attached to the roof 
structure and guy wires to anchor every- 
thing in place. 



In the adjacent illustration, the structural 
members span between available vertical 
supports. Although it was not economical 
in this case, it can be. If you use this 
approach, be sure to allow for tempera- 
ture expansion. 



totwt 




GUY 



©SK«,LJi 



Another interesting approach involved the 
use of heavy dead-load concrete blocks, 
tied together with structural members, to 
withstand the horizontal force of the 
wind. If your roof can take it, this is a 
feasible way to go, but you'll pay a 
penalty in the extra structure reguired to 
handle the dead load. 



f^=tr 






tm M&ttfiGt mwb 



Flashing and Drainage Problems— Remember that flat roofs are not flat; they pitch for 
drainage. If you decide to use sleepers or continuous curbs, there's a good chance that you 
will be cutting off the roof's natural drainage. Be sure that your roof can take puddling. 
Some roofing materials can and will deteriorate under puddled water conditions. 



If you are doing a retrofit, check 
the existing material. In a new 
installation, be sure that the cor- 
rect roofing material is specified. 







There is a tendency to put supports close 
to the roof edge to utilize as much sur- 
face as possible; this results in interfer- 
ence between the two sets of flashing. 
Allowances in detailing can correct this 
problem. 



mum 








i 



u 



4UiM 



E 






Shim Requirements- -! have already noted 
that flat roofs are not flat. They either 
pitch to drains or, in long spans, the 
beams are cambered. Therefore, the de- 
sign must allow for shimming of the 
structure. Do not leave it to the con- 
tractor. If you do not detail and specify 
the location and type, you may have 
serious problems. 



1 



• 7 A ■ 






4WM OBTAIN 



Snow Loads, Roof Maintenance, Drain Down— These items may seem unrelated; however, 
they should all be considered prior to establishing final collector support design. 



Snow Loads— If collectors 
are installed close to the 
roof, they will not only act 
as a snow fence but will 
actually cause additional 
snow accumulation. Besides 
carrying an extra load, 
buried collectors obviously 
are not going to work very 
well for the first week or 
two. If you lift them above 
the roof and let the wind do 
the shoveling, you can solve 
a lot of maintenance prob- 
lems, lower your snow load, 
and improve the efficiency 
of your collector. 



COULBCTOK 



w» 






kmrnmrnwrnimrm 




Also, if your collectors ex- 
tend over an entry or a 
walkway, please protect the 
pedestrians. I think that the 
pedestrian and your client 
will appreciate this protec- 
tion and so will OSHA. 




mtwr mm 



SNOW 



4WBWW 




Roof Maintenance— The higher you keep 
the collectors, including the structure and 
pipes, the easier it will be to maintain, 
repair, or even replace the roof in the 
future. If you provide walking surface 
accessways for maintenance personnel 
(with or without ladders), you will find 
that it will save much wear and tear on 
the roof. Collectors are often installed at 
a very shallow angle (especially in the 
South to best accommodate cooling 
loads). Limited space creates repair 
problems. The condition illustrated on 
the left would be a real "bear" to con- 
tend with. 



OWING 

pwrnscnasJ 





MAINTOUNG& 



Drain Down— When design- 
ing a draindown system, it is 
very common to draw your 
collector support and note 
on the drawings or in the 
specifications that the pipes 
must be "pitched to drain." 
In the case illustrated at 
right, the designer drew the 
collector without leaving 
enough room to install the 
pipe itself— let alone pitch 
it to drain. If you want the 
collectors and piping to 
pitch to the drain, be sure 
you detail it so that they 
can. Either pitch the steel 



or lift up the collectors so 
that the pipes can pitch. In 
addition, most people would 
like to avoid having pitching 
pipes all over the place. It 
does create a vertical 
problem in installing collec- 
tors. Many designers, 
therefore, are tempted to 
design the piping with 1/8 
inch pitch per foot. The 
allowable roof deflection on 
a normal beam is 1/10 inch 
per foot; therefore, the pipe 
pitching at certain parts of 
that span will be 1/40 inch. 
Normally, we call this a 
frozen pipe. 




WN^ 






fire r\ra\\ Y&FB&rooT 



/CTUALPIP£ 
HTCH 

FT- 



3C 




AUOfJ. ROOF 
V " 



10 F6K fOCfX 



Structural Loads— The loads that are imposed 
by solar installations are fairly well known. 
There is the dead load, the wind load (with its 
horizontal and vertical components), and the 
snow load. These loads can vary depending 
upon your design. Because of the extent of 
exterior construction, we have a new load- 
temperature expansion and contraction due 
to temperature differential. 




0TBH 



Mmmm «*> 



com*. 



too 1 



x 



*" 



M 



DEAD 





VMD104D 



6M0M1AAD 




«RUCnjRAL \JON& 



The structure could experience a differential 
temperature of 160 F between the summer 
sun and the cold of a winter night, and your 
piping could experience a 200 F differential. 
We must, therefore, address the considerable 
problem of thermal expansion and con- 
traction. 



Exmmou 



We have found few problems involving the actual structural support of the collector loads; 
however, the architectural implications of these loads sometimes go unnoticed. 



For example, if you fasten a post 
and base plate to a wood curb, you 
will have problems if you have only 
metal fasteners holding the metal 
base plate through metal flashings. 
Metal to metal to metal will un- 
doubtedly allow water to enter 
through the holes caused by the 
fasteners. In addition to the water 
problem, the back and forth motion 
caused by wind forces and temper- 
ature differentials actually can 
cause these fasteners to pull out 
slightly. If your wood is not treat- 
ed, it can deteriorate and cause 
futher problems. Also, as this post 
rocks, the base plate will tend to 
cause metal fatigue to the cap 
flashing at its edges. 



ID PAIU 

+ &0C& U&&* 



e 



&&&m 



<^> 



CAFRJWWr 

IN6ULATI0N-* 
&BAH- 




In the next case, the design called 
for a prefabricated curb bolted to 
the structure with a beam over it. 
When the beam moves back and 
forth, either because of wind load, 
expansion and contraction, or both, 
there will tend to be movement of 
the curb where it joins the roofing 
that could cause a roofing failure. 



<^> 



56AM 






INSULATION— 




An easy way to avoid this problem 
is to be sure you specify that the 
edges of the curb be secured to the 
roof structure. Also, when detail- 
ing wood curbs for construction in 
the field, be sure that you provide 
sufficient lateral strength. 



12 



A very common problem is the use 
of sleepers on a retrofit so as not 
to disturb the existing roofing— the 
sleeper is merely bolted down on 
top of the roofing. If you put a 
load onto a sleeper, over normal 
insulation, the normal insulation 
will not be able to take the com- 
pressive loads that can be applied. 
The sleeper will compress the in- 
sulation and actually shear the 
waterproofing membrane along the 
edge of the sleeper, thereby 
causing leaks. 



MSUUfKMe 

cftWHeo, 
MonfeAUi* 



9 



UWN&0N 
QtTAU* 




We can see that there is more than one way to cause a leak. If there is one thing we 
would prefer to avoid, it is having solar buildings become synonymous with leaking 
buildings. 



KNOW 

YOCIR 

COLLECTOR 

1. ITS SPECIAL 
REQUIREMENTS 

2. ITS SPECIAL 
CAPABILITIES 



Before making the final selection of a collector, 
be sure that you understand all the attributes of 
your collector. In addition to such mundane 
characteristics as collector efficiency and 
stagnation temperatures, you must consider 
other truly important characteristics, e.g., 
attachment requirements and rigidity of 
structure. 



13 



Insulation — Rigid fiberglass is a very com- 
mon insulating material. It is relatively 
low in cost, is available in sizes that vary 
up to 3 inches, and it resists high heat. It 
absorbs water, however, and if water does 
get in, you will have a radiator— not an 
insulator. Also, it cannot take the 
flexible shape very often required in solar 
installations. 



VANE6 UP ID 2> 







K&61ST6 MIOM WEAT 



A&5CX£a mV5K 



CANNOT TAKE 
FLEXI&tE 6MAP£ 



«GlDR»»5Uee 



Rigid foam is comparable in cost to fiber- 
glass for the same R value. Similar to 
glass, it too varies up to about 3 inches. 
However, it deteriorates very badly if 
exposed to high heat associated with stag- 
nation. If that is a problem, you might 
consider some sort of pipe wrap as an 
inner protection. Pipe wrap is not readily 
affected by water, but it is not water- 
proof —you cannot use it as waterproofing. 
As a matter of fact, water coming in 
contact with some rigid foams and pipe 
will cause a mild acid that will deterio- 
rate the pipe. So, it must be water- 
proofed effectively. Also, rigid foam 
cannot take the flexible shapes that we 
encounter with solar. 








flffGCTBD & 
$ HIGH H£AT 

MOT R&ADILY 
AFFfcCTED BT 

0*2 WATS*. 

cam AFfeor 

PIPIMQ 



CAN NOT TM& 
RE^lBLfc SMAP& 



to&DVMK 



14 



What are the special instal- 
lation requirements of your 
collector? One problem, 
mentioned earlier, is that 
any movement in the struc- 
ture (which must be rigid) 
will cause the collector to 
leak. 



Other collectors require 
special hardware mounting. 







^K&au\t&?ee>rec\Aitf rigid 
srfcuaufcg 





SPECIAL WARDWAfck 



Some collectors can only be 
tilted in one direction, or 
they will air bind. 




<?f°* 




CCU£CTO&CAH ONLY 
6L0P£ IN OM6 PIK6GTI0N 



Others have waterproofing 
problems— especially where 
the pipes extend out of the 
collector box. 




PIPS IN tLOT 



-6PEC/AL WATWPjO0FIM6 



15 



Sometimes collectors have 
special capabilities. Among 
these special capabilities is 
the ability to be fastened in 
very particular ways, e.g., 
at the corner. If your col- 
lector is capable of SDanning 
and being fastened at dif 
ferent places, it simplifies 
your structure. You do not 
have to have a member in 
an exact location; you have 
certc ; n flexibility. 



5P6CIAU 




FLANC* 




CeUPRKT 




MXGftf TO £ftt0U& 




Other collectors are quite 
long and require very little 
support because they are 
sufficiently rigid to take 
lateral movement. There- 
fore, put as little structure 
behind them as possible and 
use the strength of the col- 
lector. 



16 



For a successful project, provide for the 
collectors' requirements and use their 
capabilities. Whatever your collector 
problems are, you must know what mater- 
ials comprise your collector frame, sup- 
port structure, and fasteners. If there are 
any differential metals involved, there 
should be nonmetallic materials separa- 
ting them to prevent galvanic action. 




imz 



ammmAL 
mm* 



Considering that most cooling equipment 
requires liquids in the temperature range 
of 180-200 F, and that most collectors 
are very hard put to supply that type of 
energy, any loss due to piping or storage 
can make the whole system nonoperative. 



NON-OPTIMCIM COLLECTOR 
TILT OR ORIENTATION 
OF 10°± WILL AFFECT THE 
TOTAL SYSTEM PERFORMANCE 
BY LESS THAN 10%. 



HOWEVER, 

A POOR PIPING INSTALLATION 
CAN AFFECT THE TOTAL 
SYSTEM PERFORMANCE 
BY MORE THAN 50%. 



Insulations —Most insulation materials were not developed for use in solar projects. 
Although many materials are being adapted and used, they are not suitable in all cases. 
Let's look at some of the problems. 



17 



First, flexible foam is only available in 
1/2-inch or 3/4-inch thicknesses. To 
increase your R value you must add a 
second layer, thereby, doubling your cost. 
Second, the foam is affected by high heat. 
(The use of pipe wrap could help in this 
area.) Third, it is affected by the sun's 
ultra-violet rays. (It can be painted to 
protect against ultraviolet deterioration. 
If you do not paint it, it may deteriorate 
badly in six months and possibly fail 
completely within a year.) On the plus 
side, flexible foam is waterproof and is 
capable of taking any shape you wish. 



mm&pcm 




LIMITED IN 
TWICKNE^ 



MD 



AFFECTED &r 

high heat 

6amus£ 

WOT flfFBCT&D Of 
WATEf^ 



Pipe Supports -- It is very important to decide 
how to support your pipes within a solar 
collector array. 



AFFECTED Bf 
FttJNTED) 



CAfJTAKE. 
FlgXJ&Lg 




Pipes can be supported off the collector. This is 
normally done by using soldered copper nipples. 
Be very careful that the mechanic does not burn 
out the waterproof seals of the collector. This is 
a constant problem because the required solder 
is of a particularly high temperature. 



Pipes can also be supported off the collector 
support. Be sure you have designed space on the 
collector support to support the piping. You 
might consider the alternative of supporting the 
pipes off the back of the support. 




jmmmmwwm 



\&& 



The pipes can also be supported on the roof 
surface, but try to design the pipes so that the 
workmen do not use them as a platform. 





A fairly common way to support pipes is off 
other pipes, especially in reverse-return designs. 
In this case, be sure that the pipes are well 
supported, one from the other, and that they are 
both free to move. 



Another common pipe detailing problem is that when pipes are shown as lines on paper, 
nobody worries about the fact that they cross. Remember that pipes have thicknesses, 
usually 3 inches or more, and you must account for this thickness in your design. Also, be 
sure that you design enough space between collectors to allow for the installation of 
valves or expansion compensators if needed. 



Pipe Movement — We have shown that 
there could be as much as 2 to 2 1/2 
inches of movement in the pipe, and it is 
certain that they are always in opposite 
directions or at right angles. So, always 
allow for this pipe movement at change of 
direction or in extremely long lengths. 




nre 



MO&ttMT 



19 



Some of the means of compensating for 
these movements include silicone bulbs, 
bellows, braided wire or elbow configura- 
tions to the piping. Whatever method you 
choose, design it and show it. 




<£LbOH3 







wreWMOF 




PifE 



wmmcerm 



VVaterproofing --Frequently, waterproofing 
problem areas occur between collectors 
and piping at joints between pipes, change 
of direction in pipes or pipe T's, or where 
valves or monitoring equipment protrude 
through the waterproofing. Be sure that 
your design answers these problems. This 
is especially important with fiberglass 
because any water getting into it will 
lower the efficiency of the whole system 
significantly. 



20 



Do not allow open seams. 
Provide joint protection at 
all elbows and tees. 

Do not bind your pipes when 
supporting them. Be sure 
that the pipes are free to 
move, or, with pipe move- 
ment, you will tear either 
your waterproofing or your 
insulation. 

Do not support piping by 
puncturing your waterproof- 
ing, especially in terms of 
supporting the pipe directly. 
Puncturing not only destroys 
the waterproofing and 
wreaks havoc with the insu- 
lation but also allows a heat 
bridge to radiate additional 
energy. Support the pipe 
loosely on the outside of the 
waterproofing. 

Do not seal the ends of 
sheet waterproofings. Seal 
between the seams or the 
sealant will fail with move- 
ment. End seals will fail; 
seam seals tend not to fail. 

Lastly, avoid differential 
metals if you are using alu- 
minum waterproofing. Be 
sure that you have nonme- 
tallic protection to prevent 
galvanic action if you have 
steel structure or steel 
clamps. We saw one very 
attractive installation that 
had aluminum waterproofing 
and a sheet of galvanized 
steel under it with no separ- 
ation protection. That wa- 
terproofing will fail. 



Wm&COF1N& 



PQMT 





>W OPeM PRGStTDB joint 
PROTECTION 

i?CRIMP 




CONTEND 




MOVANT 



















STEEL 



%AL BG.TW66N J0INT5 

I- 




NDM- 



AVOID PIFFBKENHAL 

M£TAL3 ... Ofc PRCWID6 PfSOTSCtiaN 



21 



CONCLUSION: 



COST CONSIDERATIONS 



CONSTRUCTION 
CONSIDERATIONS 



FOR SOLAR PROJECTS 
TO BE COST-EFFECTIVE THE 
ARCHITECT/ENGINEER MUST 
ISOLATE THE DIFFERENT 
COST TRADE-OFFS AND 
CHOOSE THE MOST 
EFFECTIVE APPROACH. 



• THE A/E MUST ISOLATE ALL 
CONSTRUCTION PROBLEMS. 

• THE A/E MUST ALSO SOLVE 
EACH PROBLEM. 

• DETAILS AND SPECIFICA- 
TIONS MUST ADDRESS 
EACH PROBLEM. 



• THE A/E MUST FOLLOW UP 
WITH SUFFICIENT FIELD 
VISITS. 

• DON'T LEAVE PROBLEMS 
FOR THE CONTRACTORS 
TO SOLVE. 



We have seen that there is a lot more to designing an effective solar-assisted mechanical 
system than just choosing your collector area and mechanical equipment; a successful 
project demands a high level of attention to all details. 



22 



UNIVERSITY OF FLORIDA 

Mil! 



3 1262 09052 5261